Metal complex azo compounds have been used for many years as organic solvent soluble dyes. A survey of the listings in the “Colour Index,” a joint publication of the American Association of Textile Chemists and the Society of Dyers and Colourists (UK), reveals that with one exception all the dyes are chelates of chromium and, to a lesser extent, cobalt and iron. The sole exception appears to be the non ionic copper complex C.I. Solvent Black 49. As a consequence of these aforementioned metals being in the 3+ oxidation state, the dye chromophore is an anion accompanied by a cation derived from one of the alkali metals like sodium or, more frequently, an organically substituted ammonium ion. Because of their ionic nature, most of these dyes have a finite solubility in the lower alcohols, glycol ethers, ketones and esters and similar materials and generally lack significant solubility in aromatic or even more aliphatic hydrocarbons. These dyes also frequently bear sulfonic acid groups which usually limits their solubility in the less polar organic solvents even further. The dyes of the present invention are non-ionic and free from sulfonic acid groups.
It is therefore an advantage of some, but not necessarily all, embodiments of the present invention to provide a dye lacking sulfonic acid groups that have an unusually broad spectrum of organic solvent solubility, and may also be converted into stable aqueous dispersions with or without the assistance of conventional chemical dispersing agents.
Additional advantages of various embodiments of the invention are set forth, in part, in the description that follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.